Method of making a superconductor

ABSTRACT

A superconductor is provided as a tube made from a selfsupporting thin sheet with axial welding seam and attached to a separately made carrier, either as an outside envelope or, in case of a tubular carrier, as an inside lining, but always in intimate contact with the respective cylindrical carrier surface.

United States Patent [191 Ziemek et al.

[4 1 Jan. 1,1974

[ METHOD OF MAKING A SUPERCONDUCTOR [75] Inventors: Gerhard Ziemek,Hannover; Ernst Scheffler, Langehagen, both of Germany [73] Assignee:Kabel-und Metallwerke Gutehoffnungshutte Aktiengesellschaft, Hannover,Germany [22] Filed: Feb. 18, 1972 [21] Appl. No.: 227,367

Related U.S. Application Data [62] Division of Ser. No. 884,846, Dec.15, 1969,

abandoned.

[52] U.S. Cl. 29/599, l74/DIG. 6 [51] Int. Cl. I-I0lu 1l/08 [58] Fieldof Search 174/126 R, 126 CP, 174/28, 110 F, 107, DIG. 6; 29/599;

[56] References Cited UNITED STATES PATENTS 2,677,765

5/1954 Collins him/126x 2,740,095 3/1956 Somes 174/28 X 2,936,435 5/1960Buck 335/216 X 2,989,480 6/1961 Matthias.... 335/216 X 3,443,305 5/1969Matsuda.... 174/126 R X 3,567,846 3/1971 Brorein 174/110 F 3,657,8094/1972 Lehnert 174/107 FOREIGN PATENTS OR APPLICATIONS 1,452,825 8/1966France l74/D1G. 6 1,809,814 8/1969 Germany 174/D1G. 6 343,163 2/1931Great Britain 174/126 CP Primary ExaminerE. A. Goldberg Att0rneySmyth,Roston & Pavitt [57] ABSTRACT A superconductor is provided as a tubemade from a self-supporting thin sheet with axial welding seam andattached to a separately made carrier, either as an outside envelope or,in case of a tubular carrier, as an inside lining, but always inintimate contact with the respective cylindrical carrier surface.

1 Claim, 2 Drawing Figures METHOD OF MAKING A SUPERCONDUCTOR The presentinvention relates to a conductor made of superconductive material and toa method of making such a conductor. Low-temperature cables, also calledcryogenic cables, have been used for the transmission of electricalenergy. The conductors in such a cable are disposed in the interior of apipe or tube filled, for example, with liquid helium. Protection againstinflow of heat from the environment is provided by means of one or moreadditional pipes concentrically receiving the pipe which contains theconductors and is filled with liquid helium. For example, fourconcentrical pipes can be provided and arranged as follows: The spacebetween the innermost pipe and the second one with next larger diameteris evacuated and a high vacuum is maintained during operation. The spacebetween the second pipe and the third pipe receiving the second one is,for example, filled with liquid nitrogen in order to provide acontrolled distribution of the temperature gradient from the innermosttubetoward the outer environment. The space between the third and thelast pipe receiving the third pipe is again evacuated, and the lastoutermost pipe is presumed to assume ambient temperature. v 1

The conductors themselves for such a cable are known to include twoconcentrically disposed carriers, the inner carrier thereof has on itsouter surface a layer of particularly superconductive material while theinner surface ofthe outer carrier is likewise provided with a layer ofsuch a material. It is furthermore known, to use plural conductors in adivided, multiconductor system instead of a single conductor withcomparatively large cross sectiom'the conductors of the plurality havingrelative smaller cross section and are connected in parallel.

Generally speaking, the electrical conductors in a cryogenic'system arecomprised of a material which can assume superconductive state, or thereare provided carriers which can be layered with a material which can bebrought into superconductive state. Lead, niobium and some niobiumalloys and compounds have become known as being suitablesuperconductivematerial. Accordingly, the superconductors themselves can be made ofsuch a material. However, transmission of energy is usually restrictedto a thin layer near the surface ofa conductor because of currentdisplacement (skin effect). Therefore it suffices if a carrier is infact provided with a thin layer of such a superconductive material. Sucha layer is provided onto the carrier by means of electrolysis or vapordepositing.

, The invention has as its principal object the providing ofsuperconductor structure which has resulted from development in thatfield but leading in a different direction. In accordance with theinvention, a sheet or foil having thin wall thickness is made frommaterial being susceptible to assuming superconductive state. The sheetthus being provided is a regular metallic sheet and can be described asself supporting. The thin sheet of superconductive material is describedas self supporting to the extent that it can be handled and worked as aseparable entity, even though for practical employment it may requirebacking or support to prevent deformation. That sheet is arranged anddisposed onto one or several carriers or backing members. Such aconstruction can be made on a continuous basis and by suitable selectionof the carrier or backing member the structure can be made a flexibleone without difficulties. Essential, however, is that the thin sheet ismade separately from the carrier or backing member so as to have somestiffness at least to permit its designation as a sheet or foil. A thinsheet as cover on a carrier but having been made as separate foil orsheet is mechanically stronger, sturdier and more abrasion proof than alayer which has been deposited on a carrier by means of electrolysis orby vapor depositing.

As was mentioned above, only the outer surface regions of a conductorparticipate materially in the trans mission of electrical energy (A.C.).For this reason the sheet is selected to be very thin, for example,having a thickness of 0.03 to 0.5mm. Preferably, the thickness isselected from within the range from 0.05 to 0.2mm. Niobium and itsalloys have a higher critical transition temperature than lead where thematerial changes from the state as regular resistor to thesuperconductive state. Niobium and its alloys need to be cooled only to259 to 265C. whereas lead has to be cooled down to 267C. For this reasonniobium, its alloys and suitable compounds are preferred.

Niobium and its alloys are rather expensive so that it appears to be ofadvantage to use a thin, superconductive sheet which is reshaped into apipe or tube and adjoining edges are welded together. Such a thin-walledpipe, however, is unfortunately mechanically quite weak and not at allsturdy, i.e., it is rather easily susceptible to deformation. Usuallysuch conductors are wound on drums for transportation, but ifathin-walled sheet has been reshaped into a pipe it is necessary toselect very large drums as such thin-walled pipes must not be curvedsharply as they deform rather easily. For this reason, there must beprovided a backing member or carrier. The backing member may be providedin the interior of the thin-walled sheet tube as an outer cover on thebacking member and being firmly seated thereon; alternatively thethin-walled sheet may constitute a lining of the interior of a tubularbacking memher.

The carrier may be comprised ofa metal wire, for example, a copper wire.However, it is desirable to use a low-weight material so that a core ofplastic material such as a plastic string may be more advantagous foremployment as carrier and backing member to prevent deformation of thetubular superconductive sheet. The tubular superconductive sheet isfastened to a plastic backing member in the following manner: After thethin-walled pipe has been placed onto a plastic cylindrical or tubularcarrier, the pipe is heated whereupon the plastic expands, softens andis glued and bonded to the pipe. The carrier which is disposed in theinterior of the superconductive pipe preferably has a diameter of l to4mm.

A backing member for a thin-walled superconductive tube can be providedand connected thereto as follows: Liquid plastic is extruded onto thepipe to form a coating thereon. After solidification the tubularsuperconductor forms an interior lining of the now formed plastic tube.The superconductive structure in this case is tubular and hollow, and itis of advantage, particularly for increasing the cooling effect duringoperation to pass the coolant, such as liquid helium, through theinterior of the pipe. While the specification concludes with claimsparticularly pointing out and distinctly claiming the subject matterwhich is regarded as the invention, it is believed that the invention,the objects and features of the invention and further objects, featuresand advantages thereof will be better understood from the followingdescription taken in connection with the accompanying drawings in which:

FIG. 1 is a cross section through a superconductor on a carrier orbacking member;

FIG. 2 is a cross section through a superconductor made of a thin tapeforming the interior lining of a tubular plastic carrier or backingmember. Proceeding now to the detailed description of the drawings, inFIG. 1, thereof there is illustrated a carrier element or backing member1 which is constituted, for example, by a metallic wire such as a copperwire. In the alternative, the carrier can be made of plastic, forexample, polymethacrylic acid ester, polypropylene or a polyethylenecopolymer, polyacrylacid ester or the like.

A sheet or tape of superconductive material 2 has been deformed toprovide a tube and the long sides of such a tape have been weldedtogether preferably through butt welding. The welding seam 3 extends inaxial direction, accordingly. The sheet or tape 2 was originally flatand has been reshaped to assume tubular configuration. After weldingadjoining edges the superconductive sheet forms in fact a tube ortubular jacket which now is applied upon the carrier 1. in case the corecarrier or backing member 1 is made of plastic, conductor tube 2 isheated so that the plastic carrier therein is likewise heated and bondedto the interior wall of tube 2.

Turning now to FIG. 2 there is illustrated a different embodiment for asuperconductor in accordance with the present invention. There is atape-like sheet 4 of superconductive material which has been reshapedinto a pipe. In this case now, the resulting tube is enveloped by aplastic layer 5 likewise having the form ofa tube, the inner wall ofwhich being lined by superconductive, thin-walled tube 4. The plasticused is preferably a copolymer of polyethylene which has been modifiedby monomers. In this way one can obtain a very good bonding of themetallic pipe 4 to the inner wall of plastic tube 5.

In this embodiment, again a thin tape of superconductive sheet or foilmaterial is shaped into a tube 4. Now the plastic material about toestablish the backing member or carrier is extruded in the liquid stateonto the outside of tube 4. However, it has to be observed that in thiscase the plastic tube actually renders the cooling of the superconductortube 4 from the outside more difficult. However, is has to be ovservedalso that due to bonding of tube 4 to tube 5 the shape of the conductortube 4 is readily maintained by the stiffness of pipe 5. Therefore, itis not necessary in this case to include a carrier core in the interiorof the conductor tube 4. This, in turn, permits utilization of theinterior of thin-walled tube 4 as passage to the coolant, such as liquidhelium, to maintain the conductor tube 4 in the superconductive state.The fact that the tube 4 is clad in a heat-insulating plastic coat 5, onthe other hand, serves as an additional insulation of the cryogenicsystem against heat influx from the interior.

The invention is not limited to the embodiments described above but allchanges and modifications thereof not constituting departures from thespirit and scope of the invention are intended to be included.

I claim:

l. The method of making a superconductive arrangement, comprising:

providing a thin tape of superconductive material as a self supportingfoil, and having thickness in the range of 0.03 mm to 0.5mm;

bending the tape longitudinally into tubular configuration to obtainaxially adjoining edges;

welding the edges to obtain an axial seam; and

extruding a plastic material as carrier onto the tubular configurationso that the interior of the tubular configuration remains empty.

1. The method of making a superconductive arrangement, comprising:providing a thin tape of superconductive material as a self supportingfoil, and having thickness in the range of 0.03mm to 0.5mm; bending thetape longitudinally into tubular configuration to obtain axiallyadjoining edges; welding the edges to obtain an axial seam; andextruding a plastic material as carrier onto the tubular configurationso that the interiOr of the tubular configuration remains empty.